Announcements Register for Connect, register your iclickers - Register iclickers at https://www1.iclicker.com/ or REEF account profile - Purchase the REEF polling app, create an account, register and get a subscription at app.reef-education.com (or the app store or Google Play; you still have to register at reef-education and get a subscription) Go to Section starting Friday! No section Monday, it s the M. L. King holiday First homework assigned and available, due next Thursday at noon First reading assignment due next Tuesday, before class Permission codes: email the astro dept. manager Jenna Scarpelli, jscar@ucsc.edu, and copy me (crockosi@ucsc.edu) to get one Go to a section that works for your schedule, even if it isn t the one you are registered for. Please don t everyone bail on the Friday section!
Tutoring information, as announced in class UCSC Learning Support Center small group tutoring: Spencer Hatch Email: smhatch@ucsc.edu Sign-up: http://lss.ucsc.edu/programs/small-group-tutoring/index.html
Doing Some Night-time Astronomy Make groups of 1-4 students, with at least one digital camera (a cell phone camera is fine) in the group or at least one person willing to sketch Each day that it is clear at the end of class, we ll go to the bridge just down from this room and look at the sky near the southern and eastern horizon (directions we can see from there) Take a picture or make a sketch of what you see Be sure to include some trees or a building for reference Try to get the same trees or buildings each time Save the pictures and sketches, and we ll look at how the sky changes over the quarter
Chapter 1: The Earth in the Solar System We observe: motion of the sun and stars each day, changes in the night sky over the course of a year Putting these observed patterns together to make a 3D model of the solar system: The earth spins on its axis once each day The earth orbits the sun once each year Adding other things: moon and eclipses planets
The Earth Spins on its Axis Once Per Day Everything in the sky appears to rise and set once per day
The Earth Spins on its Axis Once Per Day Define a coordinate grid to measure the position of things (stars, the sun) on the sky, just like on earth Celestial Sphere : projection of latitude and longitude onto the sky North Celestial Pole North Pole (Earth) South Pole South Celestial Pole Celestial Equator
Celestial Sphere Celestial Sphere : projection of latitude and longitude onto the sky North and South poles of Earth line up with the North and South Celestial Poles Equator of the Earth lines up with the Celestial equator North Celestial Pole North Pole (Earth) South Pole South Celestial Pole Celestial Equator
The Earth Spins on its Axis Once Per Day As the earth rotates on its axis, the celestial sphere appears to rotate around the earth Everything in the sky appears to rise and set once per day
Constellations: Fixed Patterns of Stars Everything outside the solar system stays stationary on the celestial sphere: The stars appear in the same patterns, constellations, each time we see them Stars don t move relative to each other: constellations look the same each night as they rise and set.
Absolute vs. Local Coordinates Celestial sphere is an absolute coordinate system. Locations of the constellations on the Celestial Sphere are the same for everyone, always. North Celestial Pole South Celestial Pole Celestial Equator
Define some local coordinates: - Direction straight up is called the zenith, no matter where you are - Your horizon is always the lower edge of what you can see, no matter where you are Zenith (Up) North Celestial Pole South Celestial Pole Celestial Equator
Why is this useful? So we can describe where an object on the Celestial Sphere (like a star) appears to us in the sky Example: The North Celestial Pole is overhead at the Earth s North Pole... You are standing here, at the North Pole, looking straight up. Your zenith is the North Celestial Pole observer s zenith is up Looking at the zenith (straight up) while standing at the Earth s North Pole
Absolute vs. Local Coordinates: The North Celestial Pole is overhead at the Earth s North Pole... Celestial equator is your horizon. You never see stars in the south part of the Celestial Sphere because they are always below your horizon You are standing here, at the North Pole, looking straight up. Your zenith is the North Celestial Pole You never see this star Looking at the zenith (straight up) while standing at the Earth s North Pole
Absolute vs. Local Coordinates: The North Celestial Pole is overhead at the North Pole......but NOT in Santa Cruz (or anywhere else) Stars that rise and set along the red tracks are visible for this observer observer s zenith is up Celestial Equator horizon Stars that rise and set along the white tracks are never visible for this observer: they are always below the horizon
Absolute vs. Local Coordinates: The North Celestial Pole is overhead at the North Pole......but NOT in Santa Cruz (or anywhere else) Half circle: 180 degrees Line from horizon, through zenith, back down to the horizon 90 degrees from zenith to horizon Circle: 360 degrees
Absolute vs. Local Coordinates: The North Celestial Pole is overhead at the North Pole......but NOT in Santa Cruz (or anywhere else) Half circle: 180 degrees Line from horizon, through zenith, back down to the horizon 90 degrees from zenith to horizon Observer latitude = angle between Zenith and Celestial Equator Circle: 360 degrees
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can I see an object at: You are here 1) The North Celestial pole? A yes B no 2) The South Celestial pole? A yes B no 3) The Celestial equator? A yes B no
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can I see an object at: 1) The North Celestial pole? A yes B no 2) The South Celestial pole? A yes B no 3) The Celestial equator? A yes B no
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 1) A star that passes straight overhead (at the zenith) for someone who lives in Tokyo at 36º North latitude and 140º East longitude? A yes B no You are here
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 1) A star that passes straight overhead (at the zenith) for someone who lives in Tokyo at 36º North latitude and 140º East longitude? A yes B no Angular distance measured (in degrees) on the Celestial Sphere from the zenith to the Celestial Equator is equal to your latitude. (See slides 13,14) The observer at Tokyo is at the same latitude as you are in Santa Cruz, so their zenith points to the same place on the Celestial Sphere as yours. Therefore, if the star passes overhead for you, it also passes overhead for the friend in Tokyo. You are here Observer latitude = angle between Zenith and Celestial Equator
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 2) A star that passes straight overhead for someone who lives in Rio de Janeiro, Brazil, at 22º South latitude and 43º West longitude? A yes B no You are here Where is Brazil? Observer latitude = angle between Zenith and Celestial Equator
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 2) A star that passes straight overhead for someone who lives in Rio de Janeiro, Brazil, at 22º South latitude and 43º West longitude? A yes B no Observer latitude = angle between Zenith and Celestial Equator Hint #1: how many degrees long is the orange arc, the distance from the celestial equator to the horizon?
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 2) A star that passes straight overhead for someone who lives in Rio de Janeiro, Brazil, at 22º South latitude and 43º West longitude? A yes B no Hint #1: how many degrees long is the orange arc, the distance from the celestial equator to the horizon? Start by asking what the length of the pink arc is? Now what is the sum of the pink plus orange arcs? (What is the distance in degrees from zenith to horizon?) Your friend s latitude is 22 degrees South. Where is her zenith on the celestial sphere? What is the condition for you to be able to see that same star? Observer latitude = angle between Zenith and Celestial Equator Hint!
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 2) A star that passes straight overhead for someone who lives in Rio de Janeiro, Brazil, at 22º South latitude and 43º West longitude? A yes Observer latitude = B no angle between Zenith and Celestial Equator Hint #1: how many degrees long is the orange arc, the distance from the celestial equator to the horizon? Start by asking what the length of the pink arc is? 36 degrees Now what is the sum of the pink plus orange arcs? (What is the distance in degrees from zenith to horizon?) 90 degrees So the answer to Hint #1 is 90-36 = 54 degrees Your friend s latitude is 22 degrees South. Where is her zenith on the celestial sphere? 22 degrees below the Celestial Equator What is the condition for you to be able to see that same star? It has to be above your horizon. Hint!
Question: Santa Cruz is at 36º north latitude and 122º west longitude. From here, can we see: 2) A star that passes straight overhead for someone who lives in Rio de Janeiro, Brazil, at 22º South latitude and 43º West longitude? A yes B no Any observer can see from the Zenith to the horizon, which is 90 degrees. (See slides 9,13,14) The distance from zenith to the Celestial Equator is the observer s latitude. (Slide 14) For you, that s 36 degrees North. For your friend in Brazil, that s 22 degrees South. 90-36 = 54, so for you there are 54 degrees from the Celestial equator to the horizon. So, if a star passes overhead (at the zenith) for someone at 54 degrees south latitude, you would see that same star on the horizon. Your friend in Brazil is farther North, at 22 degrees South. So a star that passes overhead for her is at 54-22=32 degrees above your horizon.
The Earth Orbits the Sun Once Each Year The bright sky makes it impossible to see stars during the day We can only see half the stars in the sky at any time during the year: light from the sun prevents us from seeing the other half Which stars we can at night changes over the course of the year
The Earth Orbits the Sun Once Each Year We always see the stars in the same patterns (the constellations) They are at fixed locations on the Celestial Sphere But at different times of the year we see different constellations at night stars in constellations Sun
The Earth Orbits the Sun Once Each Year We always see the stars in the same patterns (the constellations) They are at fixed locations on the Celestial Sphere We also can t see different constellations at different times of the year. That s because which constellations are above the horizon during the day changes throughout the year. The Sun appears to move on the Celestial Sphere! November stars in constellations July stars in constellations Sun Sun
The Earth Orbits the Sun Once Each Year We always see the stars in the same patterns (the constellations) They are at fixed locations on the Celestial Sphere But we see different constellations at night at different times of year The Sun appears to move on the Celestial Sphere! Ecliptic: the path on the Celestial Sphere that the Sun appears to travel over the year
The Earth Orbits the Sun Once Each Year Another view: the direction faced by the night side of earth changes as the earth moves in its orbit
The Earth Orbits the Sun Once Each Year Constellation we see at night along the Ecliptic change during the year as the earth moves in its orbit Zodiac: Constellations on the Ecliptic
Earth s Axis Tilt and Seasons Big Picture: Planets (including earth) orbit the sun in a plane The earth s axis is tilted relative to the plane of its orbit by 23.5º Therefore the ecliptic, the path we see the sun take in the sky over a year, is tilted relative to the celestial equator by 23.5º
Earth s Axis Tilt and Seasons The earth s axis is tilted relative to the plane of its orbit by 23.5º Therefore how different parts of the earth are illuminated by the sun changes during the year
Seasons Northern Winter: axis tilt away from Sun.! Northern Winter = Southern Summer
Seasons Northern Summer: axis tilt toward the Sun.! Northern Summer = Southern Winter!!
Seasons Spring and Fall: axis tilt is neither toward nor away from the sun.! Southern and Northern hemispheres face the sun at the same angle.
Earth s Axis Tilt and Seasons Why does this matter? Sunlight is energy The total energy that the earth gets from the sun is the same all year The tilt of the Earth s axis changes how much of that energy any one place on earth gets over the course of a year The tilt of the Earths axis means: 1.Energy from the sun is spread over a smaller or larger area of the earth during the year: the intensity changes 2.The length of the day changes over a year: each place has more or fewer hours of illumination in each day
Earth s Axis Tilt and Seasons The tilt of the Earths axis means: 1.Energy from the sun is spread over a smaller or larger area of the earth during the year: the intensity changes
Earth s Axis Tilt and Seasons The tilt of the Earths axis means: 2.The length of the day changes over a year: each place has more or fewer hours of illumination in each day
Earth s Axis Tilt and Seasons Check out this link for a description of this figure and this one for the animation credit: Tunc Tezel
Seasons Northern Winter/Southern Summer: axis tilt away from Sun.! Southern hemisphere gets most concentrated energy from the sun. The sun s path is higher in the sky in the South and the sun is above the horizon longer.! Northern hemisphere gets least concentrated energy, the sun is lower in the sky and the days are shorter.
Seasons Southern Winter/Northern Summer: axis tilt away from Sun.! Northern hemisphere gets most concentrated energy from the sun, longest days! Southern hemisphere gets least concentrated energy, shortest days
Seasons Spring and Fall: axis tilt is neither toward nor away from the sun.! Southern and Northern hemispheres face the sun at the same angle.
Seasons Axis tilt also changes the distance of each hemisphere to the sun. Does that matter? - Distance from the earth to the sun: 150 million km (1.5 x 10 8 km) - Diameter of the earth: 13,000 km (1.3 x 10 4 km) The change in distance to the sun due to the axis tilt of any place on earth must be smaller than the size of the earth s diameter. Diameter of the earth is 10,000 times smaller than the size of its orbit. A 1% change is a factor of 1/100. So 1/10,000 is a change of 0.01% 0.01% is not very big, so the distance change caused by the axis tilt is not a big factor in the changing seasons What matters is the change in the intensity of the incoming solar energy caused the the axis tilt
The Moon and Earth What determines the appearance of the moon? What is moonlight? Why does the moon rise and set? Why does the shape of the moon (as we see it) change?
Orbits in the Solar System The earth and moon cast shadows Phases of the moon are caused by how we see the sun illuminate the moon, NOT the earth s shadow on the moon
Orbits in the Solar System The earth and moon cast shadows Phases of the moon are caused by how we see the sun illuminate the moon, NOT the earth s shadow on the moon The moon orbits the earth every 27 days Does the moon s illumination change much in a single day?
Orbits in the Solar System Zoom in: Moon orbits around around the Earth This is why we see the moon have phases Light from Sun
Orbits in the Solar System The earth and moon cast shadows When the earth s shadow falls on the moon: Lunar eclipse
Orbits in the Solar System The earth and moon cast shadows When the moon s shadow falls on the earth: Solar eclipse
Picture of the Moon s shadow on earth during a solar eclipse Orbits in the Solar System The earth and moon cast shadows When the moon s shadow falls on the earth: Solar eclipse
Orbits in the Solar System So why don t we have eclipses every month at full and new moon? The plane of the moon s orbit around the earth is tilted relative to the plane of the earth s orbit around the sun Light from Sun